【Git学习笔记】初始化Git仓库和版本回退

学习地址 http://www.liaoxuefeng.com/wiki/0013739516305929606dd18361248578c67b8067c8c017b000

什么是版本库呢？版本库又名仓库，英文名repository，你可以简单理解成一个目录，这个目录里面的所有文件都可以被Git管理起来，每个文件的修改、删除，Git都能跟踪，以便任何时刻都可以追踪历史，或者在将来某个时刻可以“还原”。

1. 初始化Git仓库

创建空目录

$ mkdir learngit
$ cd learngit
$ pwd
/d/mycode/learngit

把目录变成Git可以管理的仓库

$ git init
Initialized empty Git repository in d:/mycode/learngit/.git/

2. 添加文件到Git仓库

在 learngit 创建 readme.txt文件，内容是

Git is a version control system.
Git is free software.

然后

$ git add readme.txt
$ git commit -m "wrote a readme file"
[master (root-commit) 01f8c13] wrote a readme file
 1 file changed, 2 insertions(+)
 create mode 100644 readme.txt

3. 查看工作区状态和文件修改内容

修改的 readme.txt内容为：

Git is a distributed version control system.
Git is free software.

git status 命令可以让我们时刻掌握仓库当前的状态

$ git status
On branch master
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

        modified:   readme.txt

no changes added to commit (use "git add" and/or "git commit -a")

git diff 命令查看文件具体修改内容

$ git diff readme.txt
diff --git a/readme.txt b/readme.txt
index d8036c1..013b5bc 100644
--- a/readme.txt
+++ b/readme.txt
@@ -1,2 +1,2 @@
-Git is a version control system.
+Git is a distributed version control system.
 Git is free software.
\ No newline at end of file

版本回退

将上面的修改上传到git仓库中，经过n次的修改和上传后，git仓库已经有好多的版本了。

 git log 命令用来查看上传日志

$ git log
commit ce0986a8d1603fdeeb68e66b54ab7f696e4a602f
Author: liuchuanwei <1254428526@qq.com>
Date:   Wed Dec 14 14:50:17 2016 +0800

    modify readme.txt

commit 01f8c13a493c3fe08c7bdfceb22a19a0b5f20189
Author: liuchuanwei <1254428526@qq.com>
Date:   Wed Dec 14 14:31:19 2016 +0800

    wrote a readme file

如果嫌输出的信息太多太杂乱，可以是添加参数  --pretty=oneline

$ git log --pretty=oneline
ce0986a8d1603fdeeb68e66b54ab7f696e4a602f modify readme.txt
01f8c13a493c3fe08c7bdfceb22a19a0b5f20189 wrote a readme file

 

git reset --hard HEAD^ 回退到上一个版本，如果回退到上上个版本，则 HEAD^^ ，当然往上100个版本写100个^比较不容易数过来，所以写成HEAD～100。

$ git reset --hard HEAD^
HEAD is now at 01f8c13 wrote a readme file

这时再用 git log 命令来查看版本，发现版本 modify readme.txt 不见了，就好像你从21世纪坐时光穿梭机来到了19世纪，想再回去已经回不去了，肿么办？

$ git log
commit 01f8c13a493c3fe08c7bdfceb22a19a0b5f20189
Author: liuchuanwei <1254428526@qq.com>
Date:   Wed Dec 14 14:31:19 2016 +0800

    wrote a readme file

办法还是有的，只要找到版本 modify readme.txt 的commit_id ，即  ce0986a... ，它是用SHA1计算出的数字，用十六进制表示

 git reset --hard comit_id 回到指定 commit_id 的版本，commit_id 不用写全，只要git能确定版本就行

$ git reset --hard ce0986
HEAD is now at ce0986a modify readme.txt

要重返未来，用 git reflog 查看命令历史，以便确定要回到未来的哪个版本。

$ git reflog
ce0986a HEAD@{0}: reset: moving to ce0986
01f8c13 HEAD@{1}: reset: moving to HEAD^
ce0986a HEAD@{2}: reset: moving to ce0986
01f8c13 HEAD@{3}: reset: moving to HEAD~1
ce0986a HEAD@{4}: reset: moving to ce0986
01f8c13 HEAD@{5}: reset: moving to HEAD^
ce0986a HEAD@{6}: commit: modify readme.txt
01f8c13 HEAD@{7}: commit (initial): wrote a readme file